1. Field of the Invention
The present invention relates to a laminated rubber support assembly utilized for earthquake-proofing buildings and other structures.
2. Description of the Prior Art
As for a foundation material for protecting buildings and other structures against earthquakes, a laminated rubber support assembly as shown in FIG. 4 is known (Japanese Patent Application Disclosure No. 209347/1982). This laminated rubber support assembly 1 comprises a plurality of steel plates 2 and thin rubber plates 3 alternating with and vulcanization-bonded to the steel plates 2. In this assembly, since the ratio of the vertical spring rigidity to the horizontal spring rigidity can be greatly increased, it supports a building 4, which is a heavy object, in a stable manner and if an earthquake should occur, it allows the building to swing horizontally at a low speed with a period which is longer than the period of the earthquake, thus decreasing the input acceleration of the earthquake. Therefore, the earthquake resisting strength required of buildings can be made much lower than in the case of conventional rigid structure foundations which fix a building directly to the ground. Particularly, it facilitates the construction of high-rise buildings.
When the behavior of the rubber plates 3 of the laminated rubber support assembly 1 is observed, the following is found.
In the no-load state before the vulcanization-bonded laminate is installed, the laminate has been finished such that each rubber plate 3 is inwardly recessed with respect to the steel plates 2, as shown in FIG. 6 (a). In the installed state in which it is interposed between the building and the foundation, each rubber plate 3 is compressed and its peripheral region is arcuately bulged, as shown in FIG. 6 (b). After installation, if an earthquake should occur to cause a horizontal displacement of each steel plate 2, then, as shown in FIG. 6 (c), since each rubber plate 3 has its upper and lower surfaces bound by the steel plates 2, the whole is deformed under shearing stress. At this time, the exposed portion of the peripheral region of each rubber plate is obliquely stretched, as shown in FIG. 6 (c); however, since this peripheral region is also subjected to lateral tension from the inner region, it is in the highly tensioned state as compared with the inner region. Particularly when it is deformed to a large extent, it becomes harder, thus increasing the horizontal spring constant, a fact which decreases the earthquake-proofing capacity while causing the peripheral region to break as at 3a in FIG. 6 (c).